1. Field of the Invention
This invention relates to a method for the production of a graphite intercalation compound. More particularly, this invention relates to a method for the production of a graphite intercalation compound which, by effecting the reaction for the production in the presence of a second metal chloride besides the metal chloride destined to form the intercalant aimed at, notably shortens the time required for the synthesis of the graphite intercalation compound and permits the synthesis to be carried out effectively without using chloride.
2. Description of the Prior Art
The graphite intercalation compounds have been found to combine the chemical stability inherent in graphite and other properties with high degrees of electroconductivity proper to metals. The knowledge has encouraged numerous researches. These researches have unveiled the fact that graphite intercalation compounds have their nature governed by the kinds of intercalants inserted therein.
In the case of a graphite intercalation compound which has an alkali metal such as, for example, potassium as an intercalant, the graphite intercalation compound lacks stability in the air and yields to decomposition though it enjoys improved electroconductivity (Y. Iye et al., Phys. Rev. B, 25, 4583, 1982).
It has been reported that when an intercalant formed of antimony pentafluoride is used, the electroconductivity of the graphite intercalation compound using this intercalant is better than that of copper metal. In this case again, the graphite intercalation compound lacks stability in the air and, therefore, has much to be desired for the sake of practical applications (F. Vogel et al., Bull. Am. Phys. Soc., 21, 262, 1976).
The graphite intercalation compounds using metal chlorides as their intercalants possess such degrees of electroconductivity that fall short of that of copper metal but compare favorably with those of almost all metals and, that is more, enjoy stability in the air.
Particularly, when an intercalant of the cupric chloride is used, the graphite intercalation compound is stable not only in the air but also under water. The reaction for the intercalation of cupric chloride into graphite, however, proceeds so slowly that some tens of days are required for completion of the reaction (Takahashi et al., Glossary of Lectures for the 11th Annual Meeting of The Carbon Society of Japan, page 42, 1984). Owing to the slowness of the reaction, quantity use of the compound has proved virtually impracticable.
In the intercalation of nickel chloride into graphite, no graphite intercalation compound is obtained simply by heating graphite and nickel chloride intended as an intercalant for incorporation in the graphite layer under a vacuum. It has been known that in this case, the intercalation is obtained only when nickel chloride is sealed in under an atmosphere of chlorine and the graphite intercalation compound is not formed under a vacuum or under an atmosphere of any other gas than chlorine (S. Flandrois, Synth. Met., 3, 1, 1981).
For the production of a graphite intercalation compound using such a metal chloride as a substance for intercalation in the graphite layer, therefore, the presence of chlorine, a highly corrosive gas, in the reaction system is indispensable. Experimentally and practically it has been difficult to attain the synthesis easily.
It has been also known that in the intercalation of aluminum chloride in the graphite layer, the reaction time is considerably shorter when the sealing is made under an atmosphere of chlorine than when the sealing is made under a vacuum. Thus, the use of chlorine gas has been involved in the reaction system of this kind.
It has been further known that in the synthesis of graphite intercalation compounds using metal chlorides, when the reaction for this intercalation is carried out in the presence of aluminum chloride, etc. under an atmosphere of chlorine, the aluminum chloride, etc. forms a complex with the metal chloride intended for the intercalation and enhances the velocity of the reaction (E. Stumpp, Mat. Sci. Eng., 31, 53, 1977). This method however, poses problems that the reaction requires chlorine and the second metal chloride is added in such a large amount that it will survive in a large amount as a residue in the produced compound.